A total of over one hundred pharmacologically active alkaloids have been characterized in skin extracts of some 50 species of dendrobatid frogs. Five major classes of compounds have been defined and their pharmacology elucidated: The batrachotoxins are steroid alkaloids which prevent the inactivation of voltage-dependent sodium channels in nerve and muscle. A radioactive analog of batrachotoxin binds with high affinity to a limited number of sites in neuronal membranes. Binding and effects of batrachotoxins are potentiated by certain peptides and competitively antagonized by local anesthetics. The histrionicotoxins are spiropiperidine alkaloids which facilitate the conversion of chemosensitive sodium-potassium channels in nerves and effector cells to the desensitized state and block voltage-dependent potassium channels. The potencies of various histrionicotoxins at these two sites differ significantly with histrionicotoxin and perhydrohistrionicotoxin being nearly equipotent at a nicotinic receptor channel, but with histrionicotoxin being much more potent at the potassium channel. The pumiliotoxin-C class are decahydroquinoline alkaloids which block nicotinic